The invention concerns a method for bench testing a carburetor for an internal combustion engine.
U.S. Pat. No. 4,041,777 discloses a method for testing carburetors on a flow-testing bench using a combination of three critical flowthrough nozzles. In the method described therein, the output of the first critical flowthrough nozzle communicates with the air intake passage of the carburetor. In a critical flowthrough nozzle, fluid flows through the narrowest section of the nozzle at the speed of sound. By using such a nozzle, a predetermined, constant throughput rate of air can be maintained and directed through the carburetor for calibration purposes. The second cricital flowthrough nozzle has its input connected to the output of the carburetor, and maintains a steady pressure on the downstream side.
When testing engine carburetors, in addition to air, fuel is metered into the carburetor. Due to the presence of the fuel it is difficult to maintain a constant pressure at the output of the carburetor by using only the second critical flowthrough nozzle. The third critical flowthrough nozzle, which by-passes the carburetor, is present to supply air to the output of the carburetor for the purpose of thinning the fuel-air mixture which is supplied to the input of the second cricital flowthrough nozzle, and thereby assure a constant downstream pressure.
The head pressure, i.e. the pressure at the input of the carburetor, is measured and compared with a desired value associated with a model carburetor. If there is a difference between the measured pressure and the desired pressure, the position of the throttle valve of the carburetor is adjusted to compensate for the difference.
With the above-described method for testing a carburetor, it is not possible to perform dynamic measurements on a carburetor being tested. Specifically, it is not possible to determine the characteristics of a carburetor for throttle valve positions varied as a function of time. In order to change test conditions, reconstruction of the flow-testing bench is necessary.